7
IPsec VPN
152
The
possible
causes
are
as
follows:
•
The
certificate
on
either
side
is
not
signed
by
the
same
CA
server.
•
The
certificate's
validity
time
has
expired
or
it
has
not
yet
started
to
be
valid.
The
latter
can
happen
if
the
clock
is
set
incorrectly
on
either
the
CA
server
or
the
SEG
or
they
are
in
different
time
zones.
•
The
SEG
is
unable
to
reach
the
Certificate
Revocation
List
(CRL)
on
the
CA
server
in
order
to
verify
if
the
certificate
is
valid
or
not.
Double
‐
check
that
the
CRL
path
is
valid
in
the
certificate’s
properties.
(Using
the
CRL
feature
could
be
turned
off.)
Make
sure
also
that
there
is
a
DNS
client
configured
in
the
SEG
in
order
for
it
to
be
able
to
correctly
resolve
the
path
to
the
CRL.
Specific symptoms
The tunnel can only be initiated from one side
This
is
a
common
problem
and
is
due
to
a
mismatch
of
the
size
in
local
or
remote
network
and/or
the
lifetime
settings
on
the
proposal
list(s).
To
troubleshoot
this,
the
settings
for
the
local
network,
remote
network,
IKE
proposal
list
and
IPsec
proposal
list
on
both
sides
need
to
be
examined
to
try
to
identify
a
miss
‐
match.
For
example,
suppose
there
are
the
following
IPsec
settings
at
either
end
of
a
tunnel:
•
Side
A
Local
Network
=
192.168.10.0/24
Remote
Network
=
10.10.10.0/24
•
Side
B
Local
Network
=
10.10.10.0/24
Remote
Network
=
192.168.10.0/16
In
this
scenario,
the
defined
remote
network
on
Side
B
is
larger
than
that
defined
for
Side
A
’s
local
network.
This
means
that
Side
A
can
only
initiate
the
tunnel
successfully
towards
Site
B
as
its
network
is
smaller.
When
Side
B
tries
to
initiate
the
tunnel,
Side
A
will
reject
it
because
the
network
is
bigger
than
what
is
defined.
The
reason
it
works
the
other
way
around
is
because
a
smaller
network
is
considered
more
secure
and
will
be
accepted.
This
also
applies
to
the
lifetimes
in
the
proposal
lists.